Currently, US adults spend more than $10 billion per year on vitamins and dietary supplements, believing against most evidence that fortified gummy bears and water infused with vitamins will improve their health and well-being. Vitamins are necessary for life, the difference between healthy gums and scurvy, between strong bones and rickets. But, as the recent US Preventive Services Task Force (USPSTF) recommendation statement and updated evidence report and systematic review show, there is little evidence that supplemental vitamins and minerals prevent cancer, cardiovascular disease, or mortality. No vitamins were found to reduce death from cancer or cardiovascular disease, with multivitamins earning an I statement from the USPSTF (meaning that evidence remains insufficient to recommend for or against taking such supplements). Additionally, beta carotene was found to increase the chance of developing lung cancer in high-risk populations, earning it a D recommendation from the USPSTF (recommending against taking such supplements). A total of 84 studies were reviewed, testing vitamins in almost 700 000 people, and the rosiest conclusion is that more evidence is needed. In the face of such underwhelming benefits, what explains the number of people who regularly consume these unnecessary supplements?
According to population surveys, people take vitamins either to stay healthy, feel more energetic, or gain peace of mind. These evidence-defying beliefs are bolstered by clever marketing campaigns. Advertisements inform consumers that signs of potential vitamin deficiency include fatigue, low motivation, and thinning hair. As if that message does not resonate with enough people, they label their products with enticing names like “True Strength,” “Core Nutritionals” (6-pack abs around the corner), and “Immortal Elite Vitamin Pack” (because who would want to gain immortality in anything other than an elite manner?).
Essential nutrients plus clever marketing: it is clear why vitamin and mineral supplements are so appealing. But that begs the question of why it is so easy to market the unproven benefits of these products while it is so difficult to convince people to receive lifesaving vaccines.
There are several possible theories. First, people have a tendency to see the world in sharp dichotomies: good/bad, with me/against me. In the face of such dichotomous thinking, vitamins have been lumped into the good and healthy (vs bad and unhealthy) category. Once people view vitamins as being good and healthy, a second bit of psychology kicks in—what behavioral scientists call dose insensitivity—and they assume that something either improves health or not while ignoring the possibility that the health benefits of this product will vary depending on the dose. In alignment with this mindset, people know that consuming no vitamin C is bad for their health and that consuming a little vitamin C improves their health; therefore, additional consumption should improve health even more. The Hollywood star Mae West colorfully captured this mindset when she quipped that if a little is great and a lot is better, “then way too much is just about right!”
A third psychological phenomenon reenforces this mindset—a bias people have toward natural substances independent of whether those substances improve their well-being. For example, in one study people were given a choice between 2 medicines: one that was described as natural and the other described as being manufactured. They were also told that there was no difference in the harms and benefits of the 2 medications. Nevertheless, they preferred the natural one. Advertising agencies recognize this bias, underscoring that vitamin supplements are natural, with the implication being that they must be good for people’s health and well-being. Better yet, they emphasize that their products are “botanical.” Now, people can make up for the lack of fruits and veggies in their diets by ingesting daily supplements.
The appeal of vitamin supplements is further augmented by a fourth factor, an action bias—a desire, all else equal, to err toward harms of commission rather than omission. This action bias was brilliantly established in a study of elite soccer goalkeepers. Large studies have shown that the optimal strategy for blocking a penalty kick is to stay put rather than leaping left or right. Yet, it would feel terrible to stand by while an opponent slams a ball into the back of the net. Therefore, goalkeepers typically hurl their bodies one direction or another, consoled by the thought that when an opponent inevitably scores at least they made a heroic effort to prevent that outcome. A 2005 study illustrated a medical version of this psychology among lay people, the majority of whom say they would choose a 10% chance of dying from cancer surgery over a 5% risk of dying from leaving the cancer untreated.
People do not always prefer action over inaction, of course. Consider all of the people refusing to receive beneficial vaccines. That is why it is worthwhile to consider differences between vitamins and vaccines that might explain this shift in preference from action to inaction. For starters, people perceive vitamins as natural and vaccines as manufactured; vitamins as essential, vaccines as optional; vitamins as uncontroversial, vaccines as political. In addition, when people receive a vaccine, they experience a sore arm and, occasionally, a day or 2 of flulike symptoms. Despite all of those unpleasant feelings, they never know whether the vaccine prevented them from getting sick. By contrast, when people consume vitamins, they do not have sore arms or flulike symptoms. Instead, they experience a placebo effect: more energy, a greater sense of health and well-being. A group of experts might say that the benefits of vitamin supplements are minimal or nonexistent. But how can scientific facts compete with their lived experience?
The USPSTF has brilliantly synthesized evidence about the health effect of vitamin and mineral supplements. But the work is not over. If we want people to stop taking unnecessary vitamins and start receiving lifesaving vaccines, we need to address the psychological (and political) factors that cause people to embrace evidence-incongruent beliefs.